1. Field of the Art
This invention relates to a balloon anchor for an endoscopically inserting ultrasound probe of an ultrasound examination system, more particularly, to a balloon anchor for stopping a balloon fixedly and hermetically on and around an ultrasound scanning head which is designed to be introduced into a body cavity through a biopsy or instrument channel usually provided on an endoscope for insertion of forceps or other surgical or biopsy instruments.
2. Prior Art
Ultrasound examination systems are largely constituted by an ultrasound probe with an ultrasound transducer element and an ultrasound image observation terminal. Through the ultrasound transducer element of the probe which is positioned face to face with a body portion of interest, ultrasound pulses are transmitted into the body portion under examination, and at the same time return echoes are converted into electrical signals by the transducer element. The return echo signals from the ultrasound transducer element are transferred to the ultrasound image observation terminal and processed into video signals by predetermined signal processing operations well known in the art to display ultrasound images on a monitor screen.
In addition to external or percutaneous scan type ultrasound probes, there have been in use internal or intracavitary scan type ultrasound probes which are designed to be inserted into a body cavity and to transmit and receive ultrasound signals through an intracavitary wall. In the case of the internal or intracavitary scan type, the ultrasound probe has an ultrasound transducer element mounted on an ultrasound scanning head at the distal end of a narrow flexible cord. The flexible cord is disconnectibly connectible to an ultrasound image observation terminal through a connector means which is provided at its base or tail end.
The internal scan type ultrasound probes which are designed for direct ultrasound transmission and reception through an intracavitary wall have an advantage that an intracavitary portion under examination can be scanned from a very close position. For insertion into a body cavity, some ultrasound probes are designed to be inserted directly into a canal or duct leading to a body cavity of interest, while some other ultrasound probes are designed to be introduced into a body cavity by way of a guide means which has been inserted into the body cavity of interest beforehand. In case an endoscope is used as a guide means for an ultrasound probe, it becomes possible to carry out an overall examination or diagnosis on an intracavitary portion of interest, firstly examining the intracavitary portion through the endoscope and, if a diseased or suspicious portion is spotted by the use of the endoscope, making an ultrasound scan while monitoring the ultrasound probe through the endoscopic observation system. A biopsy or instrument channel which is usually provided on an endoscope is used as a guide means for introducing an ultrasound probe into a body cavity.
For placement in an endoscopic biopsy channel, the flexible cord of an ultrasound probe of this sort has to be thinner than the inside diameter of the endoscopic biopsy channel. Nevertheless, either the ultrasound scanning head or the connector which is attached to the head or tail end of the flexible cord may have a diameter larger than the endoscopic biopsy channel. In case the ultrasound scanning head is larger than the endoscopic biopsy channel in diameter, the ultrasound probe is placed in the endoscopic biopsy channel from its tail end before inserting the endoscope into a body cavity. On the other hand, in case the ultrasound scanning head of the probe is smaller in diameter than the endoscopic biopsy channel, the ultrasound probe can be placed in the endoscopic biopsy channel after inserting the endoscope into a body cavity to be examined.
At the time of an ultrasound scanning operation, an air gap in a path of ultrasound signals between an ultrasound transducer element and an intracavitary wall under examination could attenuate the signals to a considerable degree. In order to avoid this problem, it has been the general practice to fit on and around an ultrasound scanning head of a probe a balloon which is filled with an ultrasound transmitting medium. A balloon of this sort is composed of a flexible membrane of elastic material such as latex or the like, and a resilient stopper ring which stops the balloon on an ultrasound scanning head of a probe in a sealed state. The flexible membrane is in some cases in the shape of a bag which is closed at its fore end and open at its base end to be fitted and anchored on an ultrasound scanning head of a probe by a resilient ring. The flexible membrane of the balloon may be of a cylindrical shape which is open at its opposite ends and designed to be anchored on an ultrasound scanning head of a probe by means of a couple of resilient stopper rings.
Provided on the circumferential surface of an ultrasound scanning head of a probe is one or two annular grooves for anchoring the above-mentioned resilient stopper ring or rings. The flexible membrane of a balloon which is fitted on an ultrasound scanning head of a probe is hermetically sealed at its open end or ends as the resilient stopper ring or rings are engaged with the annular groove or grooves on the side of the ultrasound scanning head. After putting on a balloon, the ultrasound probe is inserted into a biopsy channel of an endoscope and protruded into a body cavity through an opening at the fore end of the endoscopic biopsy channel. Thereafter, an ultrasound transmitting medium is fed to the balloon on the ultrasound scanning head, filling and inflating the balloon with the ultrasound transmitting medium to a certain degree. As an ultrasound transmitting medium, for example, deaerated water or the like can be suitably used for this purpose.
During transmission and reception of ultrasound signals, the balloon which is filled and inflated with an ultrasound transmitting medium is held in intimate contact with an intracavitary wall. For instance, the sites of internal ultrasound examination by a probe usually include a narrow duct like the esophagus as well as the stomach and other internal organs. In case of an ultrasound examination within a narrow duct, the balloon can be brought into intimate contact with an intracavitary wall without sending a large quantity of ultrasound transmitting medium into the balloon. However, for bringing the balloon into intimate contact with an intracavitary wall within a body cavity which has a broad space like the stomach, it becomes necessary to inflate it to a greater degree by sending thereinto a larger amount of ultrasound transmitting medium.
The ultrasound scanning head of the probe, which is to be fitted with a balloon, normally has a rigid structure for accommodation of an ultrasound transducer element. For insertion into an endoscopic biopsy channel, the ultrasound probe is arranged to have a very small diameter even at the ultrasound scanning head, and to have a minimum necessary length in the axial direction. Accordingly, the flexible membrane and resilient stopper ring or rings of a balloon to be fitted on the ultrasound scanning head of a probe are also restricted in dimensions. Besides, since an ultrasound transducer element is accommodated in the ultrasound scanning head, the depth and width of the annular grooves which are provided on the scanning head for anchoring the resilient stopper rings are subject to similar dimensional restrictions. As a consequence, in some cases a limitation is put on the amount of ultrasound transmitting medium to be supplied to the balloon, making it difficult to hold the balloon in intimate contact with an intracavitary wall under observation over a broad area. In addition to limitation of a feasible ultrasound scanning range, due to insufficient anchoring strength of a resilient stopper ring, there has been a problem of dislocation of the resilient stopper ring out of the annular groove on the ultrasound scanner head under the weight of the supplied ultrasound transmitting medium. These problems occur more conspicuous especially in case of an endoscopically inserting type ultrasound probe which requires a balloon with flexible membrane and resilient ring of smaller sizes for passage through a biopsy channel of an endoscope.